In the case of the gyro, a specific class of gyro was identified in which the gyro bias reversed polarity when the drive and sense axes were interchanged. This particular class of gyro was identified as Class II Coriolis Vibratory Gyro and is characterized by being inherently counterbalanced, symmetrical about the input axis and having orthogonal degenerate vibration modes. Self calibration of the gyro bias is achieved by employing two gyros to measure the angular rate and sequentially reversing the gyro bias. The sequence of data from the gyros may be processed in an algorithm to solve for the gyro biases and subtract them from the measured rate. The two self-calibrated gyro angular rate measurements are averaged to reduce the angle random walk.
Self-calibration of accelerometer bias can be achieved in a manor similar to the self-calibration of gyro bias. In the case of the accelerometer the polarity of the scale factor is reversed. A method for reversing the scale factor polarity of an accelerometer is shown in U.S. Pat. No. 4,599,896, “High Accuracy Accelerometer”. Self-calibration of accelerometer bias is achieved by employing two accelerometers to measure the acceleration and sequentially reverse the accelerometer scale factor. The polarity of the accelerometer bias remains unchanged and the sequence of data from the accelerometers is processed in the previously disclosed algorithm to solve for the accelerometer biases and subtract them form the measured acceleration. The two self-calibrated accelerometer acceleration measurements are averaged to reduce the velocity random walk.
Accelerometer bias uncertainty is a major source of error in inertial measurement and navigation systems. Bias uncertainty arises due to transient behavior at turn on, non-modelablity and instability of bias versus temperature characteristics including hysteresis and simply trend over time. Reduction or elimination of accelerometer bias uncertainty would significantly improve the performance of inertial measurement and navigation systems.
There is a need in the art for improved self-calibrating accelerometers.